This invention relates to a bag having one end closed by end portions of the bag which are tucked and folded over to close said one end, a cover sheet being adhesively secured to the tucked and folded portions of the bottom. Such bags are known as cross-bottom bags.
It is already known from the practice of producing such cross-bottom bags, in particular from plastics foil, for a hot-setting adhesive which is referred to as a "hot melt" to be applied in strip form to the two corner tucks of each bottom, after the bottom square has been formed, before the side fold portions of the bottom are folded over. The length of the hot-setting adhesive coating is such that a portion thereof projects beyond the subsequent bottom fold edges of the bottom side fold portions. Subsequently, the bottom side fold portions are folded about the above-mentioned bottom fold edges, and finally a bottom cover sheet which is coated with adhesive on one side is stuck to the bottom folding, over the complete area thereof. In cross-bottom bags produced in this way, the entire sealing of the bottom as regards trickle losses, the ingress of rain water or dust or the like, is effected on the one hand by the hot melt strip on the bottom corner tucks and on the other hand by the bottom cover sheet which is applied last. The sealing action which is produced in this way has been found insufficient in practice. In particular, it has not been possible to produce cross-bottom bags which are absolutely dust-tight and which are protected from the ingress of rain water or moisture, and this has a particularly disadvantageous effect when for example fertiliser agents in dust form are to be stored in open country, which agents should naturally not come into contact with moisture which would result in lumps being formed. The same also applies as regards many other critical substances to be contained in the bags. The reason for the defective sealing in cross-bottom bags produced in the above manner is inter alia that the plastics film used in practice is generally of low folding endurance, which also is true as regards certain kinds of paper which are used for the production of paper bags, and the effective restoration forces of the relatively stiff bag material, after securing the bottom side fold portions, must be resisted alone by the coating of hot melt which was applied at the beginning to the bottom corner tucks. The above-mentioned restoration forces cannot be completely carried at the critical points at which the diagonal fold edges of the bottom side fold portions cross with the strips of hot melt, if the bottom cover sheet which is coated on one side has been fitted, as in the time between applying the strips of hot melt and fitting the bottom cover sheet the surface of the hot melt coating has already cooled to such an extent that an intimate connection between the hot melt coating and the coating of adhesive on the bottom cover sheet is no longer ensured, the coating of adhesive on the bottom cover sheet comprising a different adhesive composition from the hot melt. The consequence of this is that free passages which are not stuck occur between the inside and outside of the bag, particularly in the region between the diagonal fold edges of the bottom side fold portions in which the hot melt coating comes into direct contact with the bottom cover sheet. These free passages permit the material contained in the bag to escape, particularly when it is a dusty material, and permit moisture to penetrate into the interior of the bag.